1. Field of the Invention
This invention relates generally to the recording and reproduction of information signals, such as, for example, color video signals, and more particularly is directed to the reduction of cross-talk in the reproduction of signals recorded in adjacent tracks, even though the relatively low frequency chrominance signal compounds of color video signals are recorded for every line interval and the tracks are very close together, or even may be overlapping.
2. The Prior Art
It is well-known to record video signals on magnetic tape or other forms of record medium by scanning successive parallel tracks on the record medium with one or more transducers energized by the video signals. There has been a constant effort to improve the efficiency of use of the record medium by packing the tracks as close together as possible. The packing density has always been limited by, among other things, the fact that, during reproduction of the recorded signals, a reproducing transducer scanning each of the tracks in order could pick up signals or cross-talk from adjacent tracks.
One effort made to minimize cross-talk has been to use two transducers having air gaps with different azimuth angles for successive lines. This is relatively easy to do because most magnetic recording apparatus for video signals includes a rotary drum provided with two transducers or heads which can have gaps with different azimuth angles. The tape is wrapped helically about a portion of the perimeter of the drum and moved longitudinally along this helical path while the transducers or heads are rotated, thus bringing the heads alternately into recording relationship with the tape and allowing each head to trace out a respective one of the tracks. Each transducer or head has a finite width and thus produces magnetization of those magnetic domains in the material on the tape in what would appear to be, if such domains were visible, a series of parallel lines or stripes, each having a length as great as the width of the track, and each having an orientation that corresponds to the azimuth angle of the gap of the transducer or head used to record that track.
By recording successive alternate tracks with transducers or heads having different azimuth angles, and in view of the fact that the reproducing transducers or heads would also have corresponding azimuth angles, the gap of the reproducing transducers or heads would be aligned with the parallel, but fictitious, lines of the track being scanned thereby, but, because of the difference in azimuth angles, would extend at an angle to such lines of the next adjacent track. If the reproducing transducer overlapped that adjacent track, the well-known azimuth loss would result in attenuation of the signal reproduced from the adjacent track. Even if the reproducing transducer accurately scans a track recorded with the same azimuth, the reproducing transducer may still be influenced by the signals recorded in adjacent tracks with different azimuths, but the azimuth loss will decrease or eliminate the effect of such signals recorded in adjacent tracks on the output signal of the transducer.
Even in the above type of recording with different azimuth angles, there is still a limit to the overlapping or abutting of adjacent tracks. This is due in part to the fact that some of the recorded information may include relatively low frequencies, and the azimuth loss is generally proportional to the frequency of the signals. Thus, interference due to cross-talk from low frequency signals, such as, a frequency converted chrominance signal component, is not reduced to the same degree by the use of transducers having different azimuth angles as cross-talk from high frequency signals, such as a frequency modulated luminance signal component.
One important step in minimizing cross-talk of low frequency information is disclosed in U.S. Pat. Application Ser. No. 277,815, filed Aug. 3, 1972, now U.S. Pat. No. 3,821,787 and assigned to the assignee of the present application. In some embodiments of that earlier application, the relatively high frequency luminance components were recorded during every line area increment on every track, but the low frequency chrominance components were not recorded in adjacent line increment areas of adjacent tracks. The chrominance components were recorded intermittently, usually in alternate line intervals, but also permissibly for every third or fourth line interval or for two or more successive line intervals followed by at least the same number of line intervals in which the chrominance components were not recorded, and in all cases the recording in adjacent tracks was such that chrominance components would not be recorded in adjacent line increments of the respective tracks. If this type of recording were visible, the chrominance components would appear to be recorded in a checkerboard-like pattern. Furthermore, the luminance components could also be recorded intermittently in this same way to permit even further overlapping of adjacent tracks.
In the reproduction of signals recorded with this checkerboard-like pattern, the components that were recorded only intermittently would be utilized directly upon reproduction and would also be delayed for the length of time necessary to permit them to be used during the next succeeding interval in which similar information was not recorded. This system reduced the cross-talk interference but at some sacrifice in the quality of the reproduced image, due to the fact that less information was recorded than was available.